What Is Computer Programming?

Introduction

Today, most people don't need to know how a computer works. Most people
can simply turn on a computer or a mobile phone and point at some little
graphical object on the display, click a button or swipe a finger or two, and
the computer does something. An example would be to get weather information
from the net and display it. How to interact with a computer program is all
the average person needs to know.

But, since you are going to learn how to write computer programs, you need to
know a little bit about how a computer works. Your job will be to instruct
the computer to do things.

proc-ess / Noun:
A series of actions or steps taken to achieve an end.
pro-ce-dure / Noun:
A series of actions conducted in a certain order.
al-go-rithm / Noun:
An ordered set of steps to solve a problem.

Basically, writing software (computer programs) involves describing
processes, procedures; it involves the authoring of algorithms.
Computer programming involves developing lists of instructions - the
source code
representation of software The stuff that these instructions manipulate are
different types of objects, e.g., numbers, words, images, sounds, etc...
Creating a computer program can be like composing music, like designing a house,
like creating lots of stuff. It has been argued that in its current state it
is an art, not engineering.

An important reason to consider learning about how to program a computer is that
the concepts underlying this will be valuable to you, regardless of whether or not
you go on to make a career out of it. One thing that you will learn quickly
is that a computer is very dumb, but obedient. It does exactly what you tell
it to do, which is not necessarily what you wanted. Programming will help
you learn the importance of clarity of expression.

A deep understanding of programming, in particular the
notions of successive decomposition as a mode of analysis
and debugging of trial solutions, results in significant
educational benefits in many domains of discourse,
including those unrelated to computers and information
technology per se.
(Seymour Papert, in "Mindstorms")

It has often been said that a person does not really
understand something until he teaches it to someone else.
Actually a person does not really understand something
until after teaching it to a computer, i.e., express it
as an algorithm."
(Donald Knuth, in "American Mathematical Monthly," 81)

Computers have proven immensely effective as aids to clear
thinking. Muddled and half-baked ideas have sometimes
survived for centuries because luminaries have deluded
themselves as much as their followers or because lesser
lights, fearing ridicule, couldn't summon up the nerve to
admit that they didn't know what the Master was talking
about. A test as near foolproof as one could get of whether
you understand something as well as you think is to express
it as a computer program and then see if the program does
what it is supposed to. Computers are not sycophants and
won't make enthusiastic noises to ensure their promotion
or camouflage what they don't know. What you get is what
you said.
(James P. Hogan in "Mind Matters")

But, most of all, it can be lots of fun! An associate once said to me
"I can't believe I'm paid so well for something I love to do."

Just what do instructions a computer understands look like? And, what
kinds of objects do the instructions manipulate? By the end of this
lesson you will be able to answer these questions. But first let's
try to write a program in the English language.

Programming Using the English Language

Remember what I said in the Introduction to this lesson?

Writing software, computer programs, is a lot like
writing down the steps it takes to do something.

Before we see what a computer programming language looks like, let's use the
English language to describe how to do something as a series of steps.
A common exercise that really gets you thinking about what computer programming
can be like is to describe a process you are familiar with.

Describe how to make a peanut butter and jelly sandwich.

Rather than write my own version of this exercise, I searched the Internet for
the words "computer programming sandwich" using
Google. One of the hits returned was
http://teachers.net/lessons/posts/2166.html. At the link, Deb Sweeney
(Tamaqua Area Middle School, Tamaqua, PA) described the problem as:

Objective: Students will write specific and sequential steps
on how to make a peanut butter and jelly sandwich.
Procedure: Students will write a very detailed and step-by-step
paragraph on how to make a peanut butter and jelly
sandwich for homework. The next day, the students will
then input (read) their instructions to the computer
(teacher). The teacher will then "make" the programs,
being sure to do exactly what the students said...

When this exercise is directed by an experienced teacher or mentor it is excellent
for demonstrating how careful you need to be, how detailed you need to be, when
writing a computer program.
Here is teacher/mentor support material.

Programming Languages - High-Level Languages

Almost all of the computer programming these days is done with high-level
programming languages. There are lots of them and some are quite old.
COBOL, FORTRAN, and Lisp were devised in the 1950s!!! As you will see,
high-level languages make it easier to describe the pieces of the program you are
creating. They help by letting you concentrate on what you are trying to do
rather than on how you represent it in a specific computer architecture. They
abstract away the specifics of the microprocessor in your computer.
And, all high-level languages come with large sets of common stuff you need to do,
called libraries.

In this introduction, you will work with two computer programming languages:
Logo and Java. Logo comes from Bolt, Beranek & Newman (BBN) and
Massachusetts Institute of Technology (MIT).
Seymour Papert, a scientist at MIT's Artificial Intelligence Laboratory,
and co-workers championed this computer programming language in the 70s. More
research of its use in educational settings exists than for any other programming
language. In fact, the fairly new Scratch
Programming Environment (also from MIT) consists of a modern graphical user
interface on top of Logo-like functionality.

Java is a fairly recent programming language. It appeared in 1995 just
as the Internet was starting to get lots of attention. Java was invented
by James Gosling, working at Sun Microsystems. It's sort-of a medium-level
language. One of the big advantages of learning Java is that there is a lot
of software already written (
see: Java Class Library) which will help you write graphical programs that run
on the Internet. You get to take advantage of software that thousands of
programmers have already written. Java is used in a variety of applications,
from mobile phones to massive Internet data manipulation. You get to work
with window objects, Internet connection objects, database access objects and
thousands of others. Java is the language used to write
Android apps.

So, why do these lessons start with the Logo programming language? No other
language has the depth of research devoted to its use in educational settings.
Hundreds of books and research papers have been written regarding its use in the
classroom.
Cynthia Solomon, who started MIT's Logo Group with Dr. Papert, has put together
a comprehensive website on Logo:
logothings.wikispaces.com.

I like using the Logo language to teach introductory programming because it is very
easy to learn. The faster you get to write interesting computer programs the
more fun you will have. And... having fun is important! But do not let
Logo's simplicity fool you into thinking it is just a toy programming language.
Logo is a derivative of the Lisp programming language, a very powerful language
still used today to tackle some of the most advanced research being performed.
Brian Harvey shows the power of Logo
in his Computer Science Logo Style series of books.
Volume 3: Beyond Programming
covers six college-level computer science topics with Logo.

Both Logo and Java have the same sort of stuff needed to write computer programs.
Each has the ability to manipulate objects (for example, arithmetic functions for
working with numbers). Each lets you compare objects and do a variety of things
depending on the outcome of the comparison. Most importantly, they let you define
named procedures. Named procedures are lists of built-in instructions and
other named procedures. The abstraction of naming stuff lets you write programs
in a language you yourself define. This is the stuff that programming is really
all about, as you will see.

Just to give you a feel for what programming is like in a high-level language,
here's a program that greets us, pretending to know English.

print [Hello world!]

This is one of the simplest programs that can be written in most high-level languages.
PRINT is a command in Logo When it is performed, it takes
whatever follows it and displays it. The "Hello world" program is famous;
checkout its description on
Wikipedia by clicking here.

In addition to commands, Logo has operators that output some sort of result.
Although it's a bit contrived, here is a program that displays the product of
a constant number (ten) and a random number in the range of zero through fourteen.

print product 10 (random 15)

In this source code, the PRINT command's input is the output of the PRODUCT
operator. PRODUCT multiplies whatever follows it by whatever follows that
and outputs the result. So, PRODUCT needs two inputs. RANDOM
is an operator that outputs a number that is greater than or equal to zero (0) and less
than the number following it. So, PRODUCT gets its second input from the
output of RANDOM.

Confusing?

Figure 1.1 shows a plumbing diagram, a graphical representation of
how all these procedures fit together.

Figure 1.1

Still confusing? Don't worry, we will get into the details of Logo
operators in lesson 8.

Finally, here's a snipet of advanced Logo source code, just to give you a feeling for
what it looks like. This is a procedure definition for selecting the maximum
number from a list of numbers.

Again, do not worry if you do not understand exactly how this procedure works.
It will be a while before you will be writing anything like this. But, I want
you to see that the words that make up the program's instructions and the instructions
themselves are similar to English sentences, e.g., the first line and a half in the
procedure are similar to the sentences:

If the list of numbers to process is empty then output the maximum number processed.
If the first number in the list is greater than the maximum number processed so far then ...

So, a high-level programming language is *sort-of* like English, just one step
closer to what the language a computer really understands looks like. Now
let's move on to what a computer's native language looks like when it is given
a symbolic representation.

Programming Languages - Assembler Language

One abstract layer above a computer's native language is assembler language.
In assembler language, everything is given human-friendly symbolic names.
The programmer works with operations that the microprocessor knows how to do,
they have symbolic names. The microprocessor's registers and addresses in
the computer's memory are also given meaningful names by the programmer.
This is actually a very big step over what a computer understands, but still
tedious for writing a large program. Assembler language instructions still
have a place for little snipits of software that need to interact directly with
the microprocessor and/or those that are executed many, many, many times.

Table 1.1 is an example of DEC PDP-10 assembler language, a function that
returns the largest integer in a group of them, named NUMARY. The group
contains NUMNUM members.

Label

OpCode

Register

MemoryAddress

IndexRegister

Comment

GETMAX:

MOVSI

T1

400000

; init T1 to smallest integer

MOVE

T2

NUMNUM

; get number of array members

GTMAX2:

SOJL

T2

[POPJ P,]

; decr idx, if -1 then done

CAMG

T1

NUMARY

(T2)

; skip if T1 > array member

JRST

GTMAX2

; continue with next number

MOVE

T1

NUMARY

(T2)

; T1 gets new max number

JRST

GTMAX2

; continue with next number

Table 1.1

Hopefully this gives you feel for how primitive computer instruction sets are.
I'm not going to go into the details of every instruction. If you want to go
through it in detail on your own,
the PDP-10
Machine Language is detailed here.

A few points I want to expose you to are the general kinds of things being
done.

comparing the contents of a register to some value
in the computer's memory, and

transfering control to an instruction that's not in the
standard sequential order - down the page.

So, as you've seen, higher-level programming languages provide similar
functionality and in a form that is closer to the English language.

But there is a problem with assembler language - it is unique for every computer
architecture. Although most deskside and notebook computers these days use the
Intel architecture, this is only recently the case. And... a variety of computer
architectures are commonly used in game systems, smart phones, tablets, automobiles,
appliances, etc...

Ok, we are almost at a point where I can show you machine language, the *native*
language of a computer. But for you to understand it, I'm going to have to
explain how everything is represented in a computer.

Inside Computers - Bits and Pieces

Your computer successfully creates the illusion that it
contains photographs, letters, songs, and movies. All it
really contains is bits, lots of them, patterned in ways
you can't see. Your computer was designed to store just
bits - all the files and folders and different kinds of
data are illusions created by computer programmers.
(Hal Abelson, Ken Ledeen, Harry Lewis, in "Blown to Bits")

Basically, computer instructions perform operations on groups of bits.
A bit is either on or off, like a lightbulb. Figure 1.2_a shows an open
switch and a lightbulb that is off - just like a transistor in a computer represents
a bit with the value: zero. Figure 1.2_b shows the switch in the closed
position and the lightbulb is on, again just like a transistor in a computer
representing a bit with the value: one.

Figure 1.2_a

Figure 1.2_b

A microprocessor, which is
the heart of a computer, is very primitive but very fast. It takes groups
of bits and moves around their contents, adds pairs of groups of bits together,
subtracts one group of bits from another, compares a pair of groups, etc...
- that sort of stuff.

Inside a microprocessor, at a very low level, everything is simply a bunch of
switches, also known as bits - things that are either on or off! Time to
expand on how this is done; first let's explore how groups of bits can be used
to form numbers.

Numeric Representation With Bits

There are only 10 different kinds of people in the world:
those who know binary and those who don't.
- Anonymous

Computers are full of zillions of bits that are either on or off.
The way we talk about the value of a bit in the electical engineering and
computer science communities is first as a logical value (true
if on, false if off) and secondly as a
binary number
(1 if the bit is on and 0 if it's off). Most bits in a computer are
manipulated in groups, so we humans need a way to describe groups of bits,
things/objects a computer manipulates. Today, bits are most often
grouped in quantities of 8, 16, 32, and 64.

Think about how you write down sequential numbers starting with zero: 0, 1, 2,
3, 4, 5, 6, 7, 8, 9, 10, 11, etc... Our decimal number system has ten
symbols. In this sequential series, when we ran out of symbols, we combined
them. You learned how to do this so long ago, in grade school, that today
you just naturally think in terms of single digit numbers, then tens, hundreds,
thousands, etc... The decimal number 1234 is one thousand, two hundreds,
three tens, and four units.

So, how does the binary number system used inside computers work?

Well, with only two symbols, we would write the same sequential numbers as
above: 0, 1, 10, 11, 100, 101, 110, 111, 1000, 1001, 1010, 1011. The
decimal number 1234 in binary is 10011010010.

Since even reasonable numbers that we use all the time make for very long
binary numbers, the bits are grouped in 3s and 4s which are simple to
convert into numbers in the octal and hexadecimal number systems.
For octal, we group three bits together. Take the binary equivilent
of decimal 1234, 10011010010, and put spaces in between each group of
three bits - starting at the right and going left.

10011010010 = 10 011 010 010

Now use the symbols 0, 1, 2, 3, 4, 5, 6, and 7 (eight symbols, so OCTAL)
to replace each group.

10 011 010 010 = 2 3 2 2 = 2322

The octal representations of the binary patterns are certainly easier to
read, write, and remember than the binary counterparts. An even more
compact representation can be achieved by grouping the bits in chunks of
four and converting these to hexNumerals.

When you group four bits together and use sixteen symbols (0, 1, 2, 3,
4, 5, 6, 7, 8, 9, 0, A, B, C, D, E, and F) as their abbreviations, you
have a hexadecimal representation.

10011010010 = 100 1101 0010 = 4D2

As you continue to explore how computers work, you'll hear more about
numbers expressed in octal and hex; these are just more manageable
representations of binary information - the digital world.

So, if the most common groupings of bits in a computer are 8, 16, 32,
and 64, what kinds of numbers can these groups represent?

A group of eight bits has binary values 00000000 through 11111111, or
expressed in decimal 0 through 255. A group of sixteen bits has
binary values 0000000000000000 through 1111111111111111, or decimal 0
through 65535. I'm not going to type in binary representations for
groups of 32 and 64 bits. The range of decimal values for a group
of 32 bits is 0 through 4,294,967,295. The range of decimal values
for a group of 64 bits is 0 through 18,446,744,073,709,551,615 - or
almost eighteen and a half quintillion.

But wait... these numbers are all positive (Whole Numbers). If
we are going to allow for subtraction operations on numbers, which can
result in negative numbers, we need Integers. Modern computers use
one bit in each of the groups to represent the sign (positive or negative)
when the groups are used to represent integers. Table 1.3
shows the range of numbers that can be represented with groups of 8, 16,
32, and 64 bits.

Number of Bits

Unsigned Maximum Value

Signed Minimum Value

Signed Maximum Value

8

255

-128

127

16

65535

-32768

32767

32

4,294,967,295

-2,147,483,648

2,147,483,647

64

18,446,744,073,709,551,615

-9,223,372,036,854,775,808

9,223,372,036,854,775,807

Table 1.3

That's about as deep as I want to get into the representation of numbers in
computers and the binary, octal and hexadecimal number systems. Yes,
computers have division operators but I am not going to cover numbers that
include fractional parts, i.e., the "rational" and "irrational"
numbers due to the complexity of their implementations. If you want to
read more, I googled and found what looks like a good place for you to read
more. Start at
All About
Circuits - Systems of numeration and read through it and continue on for
a few more web pages in the series.
The link to
binary number at the start of this section points to a Wikipedia page
that also will give you additional depth including the history of the binary
number system.

Symbols as Bits - ASCII Characters

Ok, so numbers are simply groups of bits. What other objects will the
computer's instructions manipulate? How about the symbols that make up
an alphabet?

It should come as no surprise that symbols that make up alphabets are
just numbers, groups of bits, too. But how do we know which numbers
are used to represent which symbols, or characters as I'm going to call
them from this point on?

It's all about standards. In these lessons, we will use the American
Standard Code for Information Interchange (ASCII) standard. It is so
ubiquious that it even has its own web page,
www.asciitable.com.

Let's walk through a couple of examples, entries in the table. Here
are some characters, their decimal value and their binary value which is
then transformed into an octal number.

Check Your Understanding So Far

Pixels

The image on your computer's display (actually all digital stuff) consists of a
bunch of colored points called pixels. A pixel is an object. It has
a color and a position (its coordinates) which consists of the row and column it
is at. Figure 1.3 shows an artist's rendition, a magnification of a
display with a circle drawn in yellow. The tiny black dots are the pixels
and the big yellow dots are the pixels that have been colored.

Figure 1.3

As an example, to display a thin vertical line, the color values of a column of
pixels are set to the desired color of the line. If you want a thicker
vertical line, you set the color values of the pixels of a group of consecutive
columns to the desired color. Figure 1.4 shows a red line that's a single
pixel wide and an orange line that's three pixels wide. The orange line is
actually a very thin rectangle.

So, the location of each pixel is obviously specified by a pair of numbers; what
about the pixel's color?

Well... a pixel's color is also specified as numbers, three of them, called RGB
(Red, Green, Blue) values. Play with the following Java applet which lets
you see what number values generate which colors. What color do you get if
you set red to 170, green to 85, and blue to 255? What's the RGB value for
your favorite color?

Color Numbers Applet

So, just as groups of bits represent numbers and symbols, they are used to
form pixels.

Optional exploration: Why red, green, and blue? Why these colors?

There are many good explanations on the Internet. If you are interested,
search the net or checkout the Wikipedia entry for
color vision.

Ok... I've exposed you to a variety of objects that you commonly see
when you are using a computer, things that can be manipulated with
instructions in a computer programming language. Now let's move on to
the computer's instructions, one more thing that is just a bunch of bits!

Programming LanguagesThe Microprocessor's Language

So, all a computer has in it is bits. You've seen how they are used
to represent stuff, pixels, numbers and characters. I've mentioned
that computers perform operations on the bits, like move them around, add
pairs of them together, etc... One final obvious question is: how
are instructions that a computer performs represented?

Well, if you instructed a computer in its native language (machine language),
you would have to write instructions in the form of (yes, once again)
binary numbers. This is very,
VERY hard to do. Although the pioneers of computer science did this, no
one does this these days.

Just to give you something to look at, just to compare, Table 1.5 shows
what the assembler language program in Table 1.1
could look like assuming that the machine instructions are loaded into memory
at addresses 100 through 107. Also, the group of numbers starts at
memory address 111 and the size of the group is in memory address 110.

Address

OpCode

Register

MemoryAddress

IndexRegister

100

205

1

400000

101

200

2

110

102

361

2

107

103

317

1

111

2

104

254

102

105

200

1

111

2

106

254

102

107

263

17

Address

Value

110

67

111

47316

. . .

177

2751

Table 1.5

A detailed explanation of any computer's instruction set is beyond what can be presented
here. I just wanted you to see how the symbolic information in assembler language
programs needs to be converted to numbers (bits) before a computer can perform it.

Debugging

No introduction to computer programming would be complete without at least mentioning
debugging. The term refers to the discovery and correction of mistakes in
computer programs. The computer is doing what you instructed it to do, not what
you meant it to do. If you enjoy puzzles, there's a good chance you will find the
process of debugging an interesting challenge.

The origin of the term came from a bug (a moth) found in a relay of a computer in 1947,
by Admiral Grace Murray Hopper.
She found why her program was not working.

Figure 1.5

Debugging is a process. The good news for us is that mistakes in introductory level
programs are not that hard to diagnose and fix. It's basically narrowing in on the
instruction, or two, that are not doing what you intended. Steps you take are like
solving Sudoku or Mastermind
puzzles.

Debugging a program can be done in steps that match the Scientific Method.

Observation,

Hypothesize,

Make predictions, and

Test

In the observation step, you think hard about what is happening versus what you expected
to be happening. An example is a program that is drawing something, but the jumble
of lines you see on the display does not look right. Or, your program has a button
that doesn't do anything when you click on it. As a programmer, you approach these
bugs like the legendary Sherlock Holmes approached his cases. Review the program
you've written and ask questions like: "How could these instructions produce what is
happening?"

Observation should lead you to the point where you can make a hypothesis about the bad
behavior. For the drawing not coming out right, a hypothesis might be something
like: "If computing the metrics (orientation, length, ...) of the first line is off, that
might produce what I'm seeing." For a button not working, a hypothesis could be:
"If the mouse's location when it is clicked is computed wrong, the program will ignore
the click." The hypotheses made are often based on intuition. This is because
usually the person debugging either wrote the program or at least modified it.

Given a hypothesis, the next step is to figure out how to test it by predicting what
should be happen if the hypothesis it correct. Continuing with the example of the
misbehaving drawing program, let's say that you notice some source code that might not
produce proper results if what it is given is not in the bounds expected. This
code could produce strange results. This is a prediction.

Finally, either the program is modified or a debugging feature in the programming
environment is used to test the prediction. Modification of the program can be
the addition of instructions that print stuff on the display. Most programming
environments include debugging features, like tracing or
setting breakpoints to suspend a program to examine its internal state. Either way,
the programmer gathers more information about what the program is actually doing, which
is, in the case of bugs, not what you expect.

Testing, even if it does not provide an answer, gets you additional information that can
be used to repeat the process. You narrow your exploration until you find your
mistake.

Finally - Who was the first computer programmer?

Ok... since you are reading this, accessing this web page on the net, you have Google
and it takes a fraction of a second to answer this question.

Ada Lovelace, was an English mathematician and
writer chiefly known for her work on Charles Babbage's
early mechanical general-purpose computer, the Analytical
Engine. Her notes on the engine include what is recognised
as the first algorithm intended to be carried out by a
machine. Because of this, she is often described as the
world's first computer programmer.

Summary

Computer programming is composing/authoring of a process/procedure for
doing something, the source code representation of algorithms - in great detail.

proc-ess / Noun:
A series of actions or steps taken to achieve an end.
pro-ce-dure / Noun:
A series of actions conducted in a certain order.
al-go-rithm / Noun:
An ordered set of steps to solve a problem.

Since computers do not understand English and it would be impossible for a human to write
a large program as a series of binary numbers that the computer can understand, we need
something in between. High-level programming languages currently fit in this category.
Given a programming language that you have chosen, you then follow its rules for
composing statements (or expressions) that instruct the computer to do what you want.

Because a computer is simply a very fast manipulator of bits (ones and zeros), through the
the power of abstraction, computer scientists have layered levels of object representation
and functionality, one on top of another. We have now been working on refining and
extending these layers for over half of a century. Table 1.6 should give you a
feel for where we stand with computer programming languages today.

In the next lesson you'll start to write programs in Logo!

Application-Specific Language(4GL)
Examples: Mathematica, SQL

High-Level Language
Examples: Logo, Python

Low-Level Language
Example: C

Assembler Language
Example: Intel X86

Machine Language
Example: Intel X86

Table 1.6

Exercises

Gabriele Cirulli has created a
game, very popular at the moment, which will teach you the powers of two
(the binary number system) as a side effect. But beware, the game
has been tagged very addictive.